(1) Field of the Invention
The present invention relates to a silver halide photographic material containing new dye image-forming couplers capable of coupling with the oxidation product of an aromatic primary amine developing agent.
(2) Description of the Prior Art
It is known that when a silver halide photographic material undergoes color development after exposure, the oxidation product of an aromatic primary amine developing agent reacts with couplers to form indophenol, indoaniline, indamine, azomethine, phenoxazine, phenazine, and other similar dyes, thereby forming color images. In this system, the color reproduction is usually accomplished by a substractive color process which employs silver halide emulsions selectively sensitive to blue, green, and red and dye image forming agents for yellow, magenta, and cyan which are complementary to the three colors respectively.
In the case of a multilayer color photographic material, it is necessary to fix the respective couplers in discrete layers so that color mixing is reduced and the color reproduction is improved. There are many known methods for rendering the couplers nondiffusible. According to one of the methods, a long-chain aliphatic group is introduced into a low-molecular weight coupler for the prevention of diffusion. The coupler produced by this method is not miscible with an aqueous solution of gelatin; therefore, it has to be solubilized in an alkali prior to being added to a gelatin solution, or it has to be dissolved in a high-boiling organic solvent for emulsification and dispersion into an aqueous solution of gelatin. A color coupler as the one described above, has the disadvantage of causing crystals to separate out in the emulsion. When a high-boiling organic solvent is used, it is necessary to employ a large amount of gelatin because the solvent softens the emulsion layer. This conflicts with the desire to reduce the thickness of the emulsion layers.
Another method of introducing couplers into discrete layers is to use a latex of a polymer coupler obtained by the polymerization of a monomer coupler. Adding a polymer coupler in latex form to a hydrophilic colloid composition has many advantages over other methods. First of all, the latex containing a hydrophobic material does not impair the strength of the film formed. In the second place, the latex containing a coupler in high concentrations permits the emulsion to contain couplers in high concentrations. In the third place, the emulsion layer can be made thin because the latex only minimally increases the viscosity of the emulsion. This thin layer contributes to an improved sharpness. Lastly, being non-migratory, the latex does not bring about color mixing, nor does it cause the coupler to separate out in the emulsion layer.
As for the polymer coupler in latex form to be added to the gelatin-silver halide emulsion, there are processes disclosed for the production and a four-equivalent magenta polymer coupler latex, for example, in U.S. Pat. Nos. 4,080,211 and 3,451,820. In British Pat. No. 1,247,668, there is disclosed a latex of a copolymer of a coupler with a competing coupler in West German Pat. No. 2,725,591 and U.S. Pat. No. 3,926,436. Further, in U.S. Pat. No. 3,767,412 and Research Disclosure 21728 (1982) there is disclosed a cyan polymer coupler latex.
In spite of the above-mentioned outstanding features, the polymer coupler still has the following problems to be solved.
(1) The polymer coupler having a comparatively high molecular weight (greater than about 10,000 in number-average molecular weight) is satisfactory in non-migratory properties; but it is poor in coupling reactivity and hence it produces a dye which is low in sensitivity, gradation, and density.
(2) When the polymer coupler contains the coupler units (the recurring units having the coupler residue) in high concentration, it extremely decreased in color-forming property per unit weight (of the coupler units).
(3) The polymer coupler of low molecular weight produces a dye of high density but is unsatisfactory in non-migratory properties. For this reason, it causes color mixing and it decreases the sensitivity.
If a polymer coupler containing the coupler units in high concentrations is capable of maintaining a color-forming property, it would only be necessary to add a small amount of coupler in high concentrations to the emulsion. This would make it possible to reduce the thickness of the sensitive layer and to considerably improve the sharpness of the image. Therefore, it is important to improve the color-forming property of a polymer coupler containing coupler units in high concentrations. It is also important to reconcile the non-migratory properties and coupling reactivity of a polymer coupler.